This invention relates to attachments for spectacles and more particularly to clip-on attachments that superimpose auxiliary optical elements in front of the lenses of spectacles.
The optical properties of a particular pair of eyeglasses are fixed at the time of manufacture. The needs of the owner of the eyeglasses with respect to vision correction or vision modification vary under different conditions. For example, reduction of light intensity as provided by sunglasses is desirable at certain times and locations but not at others. In some situations, such as where a person is operating a computer, a temporary increase in magnification can be helpful. Wearing of yellow tinted glasses can aid night vision but this may not be desirable during the daytime or in the presence of indoor lighting.
Obtaining two or more pairs of eyeglasses for use under different conditions is costly, particularly in the case of prescription eyeglasses that are fabricated to meet the specialized needs of the particular person. It is simpler and more economical to make use of attachments of the type that can be temporarily clipped onto the person's basic vision correcting eyeglasses at times when reduced light intensity or some other vision modification is needed. Clip-on devices may be manufactured in a range of sizes and optical effects (e.g., sunglasses, magnifiers, etc.) that are intended to engage the frame of a spectacle assembly. Prior clip-on eyeglass accessories of this kind have not been entirely satisfactory for several reasons. For example, eyeglasses are made in a variety of sizes and a variety of configurations, and these configurations tend to vary from time to time because of changes in fashion or the introduction of new materials. Many prior clip-on accessories are mass produced in one size and shape or a limited number of sizes and shapes. Consequently the optical elements of such accessories often do not have the same configuration and spacing as the lenses of the eyeglasses with which they are used. This disconformity can cause several problems. Undersized optical elements and optical elements that are out of register with the eyeglass lenses tend to disrupt the wearer's field of view and also present an unaesthetic appearance to others. Oversized optical elements may contact the wearer's skin in an irritating manner and have projecting edges that may promote dislodgement of the accessory from the eyeglasses.
One solution to these problems known in the prior art is the introduction of customized clipon accessories for eyeglasses, as described in U.S. Pat. No. 5,123,724, issued to the present inventor. The customized items employ accessory lenses cut or otherwise shaped to conform to the outer perimeter of the eyeglass lenses, and clasp components that are permanently secured to the accessory lenses. The clasp components include bracket portions that engage the frame or lenses of the eyeglasses, and a bridge member that joins the upper clasps and unites two accessory lenses into a single assembly. The custom accessory lenses and the choice of the proper bridge member length provides an exact fit that obviates many of the problems noted above.
The patented methodology calls for the use of an adhesive component to join the clasps to the peripheral edge portion of the accessory lens. Although this expedient works quite well, it has been found that the process of applying adhesive and then crimping the clasp onto the accessory lens may cause some of the adhesive to exude onto the accessory lens. This requires an additional cleanup step that must be carried out quickly, before the (usually fast-setting) adhesive cures or sets. There is a need in the prior art for a custom clip-on eyeglass accessory construction that overcomes this problem.